This invention relates to heating systems for automotive passenger vehicles. A principal object is to speed up the delivery of heat to the heater and the windshield defroster on a cold day. Commonly used prior art automobile heating systems rely upon heat generated in the engine. This heat is transferred to a liquid coolant which is routed through a heater core located in the passenger compartment.
During normal operation of the vehicle the coolant is directed through a connected series of internal engine passages. These passages are connected to a radiator which cools the engine by transferring excess heat from the coolant to the outside environment. When the engine is started from an initially cold condition, it passes through an engine warm-up phase during which the coolant bypasses the radiator. This conserves energy and speeds up the onset of smooth, normal operation.
On a cold day the engine warm-up phase continues for about 15 minutes, the coolant is insufficiently hot for warming the passengers or defrosting the windshield until after that period of time has elapsed. This is especially true for vehicles equipped with diesel engines. In the future, as engines become more efficient, smaller amounts of excess engine heat will be generated. This then will further prolong the engine warm-up time.
Several methods are currently employed for decreasing vehicle warm-up time. One such method involves using an electric heater in line with the pre-existing heat exchanger. This arrangement decreases vehicle warm-up time, but it requires a substantial increase in electrical power supplied by the alternator. As a practical matter, the surplus electrical power available for servicing such a heating system is limited to about 1.0 kw. Other known methods for increasing heat to the passenger compartment include gas fired heaters, viscous shearing devices, and electric seats.
This invention speeds up the operation of an automotive heating system by providing a novel local heat generator in the form of an orifice of appropriate size. A working fluid, preferably an oil such as power steering fluid, is heated by pumping it through the orifice at an appropriate mass flow rate. A 5-10 KW hydraulic pump is considered to be suitable for this purpose. The invention may be practiced through the use a dedicated pump, but a shared pump also could be used. A suitable shared pump could provide pressurized hydraulic fluid flow for other functions such as power steering, braking or radiator fan operation. Heat energy, delivered to the working fluid during passage through the orifice, is transferred to an airstream flowing through the passenger compartment, thereby warming the occupants and defrosting the windows.
In a first embodiment of the invention the working fluid is a hydraulic fluid, which flows through an oil-to-coolant heat exchanger, following passage through the orifice. As the working fluid passes through the oil-to-coolant heat exchanger, it heats a liquid coolant which is passing concomitantly therethrough. The liquid coolant flows through a coolant-to-air heat exchanger situated in the passenger compartment. A blower fan then heats the passenger compartment by blowing ambient air across heat transfer surfaces in the coolant-to-air heat exchanger. Meanwhile the engine is being separately heated by another flow of liquid coolant flowing in a loop which has a direct return to the engine.
Further, in the first embodiment there is a thermostatic valve which directs the return flow of liquid coolant through a radiator when the engine has been heated to a suitably high operating temperature. There is also a bypass valve for isolating and circulating a fraction of the liquid coolant, independently of the main engine coolant circuit. This reduces the thermal mass of the liquid coolant used for heating the passenger compartment, thereby increasing the speed of warm-up.
A second embodiment of the invention also uses hydraulic oil as a working fluid. However, two heat exchangers are mounted in the passenger compartment; one of which exchanges heat from oil to air; and the other of which exchanges heat from coolant to air. There is no heat exchange from oil to coolant. The two heat exchangers are positioned in tandem, so that air can be blown in sequence over the two sets of heat exchange surfaces.
In a third embodiment of the invention an oil-to-air heat exchanger and a coolant-to-air heat exchanger are placed side-by-side. Air flow is provided by single blower and suitable ductwork.